1. Field of the Invention
The present invention relates to an illumination apparatus used for an exposure apparatus. The illumination apparatus uses a light source that emits light in the extreme ultraviolet (EUV) range of 200 nm to 10 nm or in the X ray range. The illumination apparatus exposes an object such as a monocrystal substrate for a semiconductor wafer or a glass substrate for a liquid crystal display (LCD). The present invention also relates to an exposure apparatus and a method for manufacturing a semiconductor device.
2. Description of the Related Art
Japanese Patent Laid Open Application No. 11219900 discloses a masking blade that includes a variable blade for restricting the field. The variable blade is disposed adjacent to the underside (the side on which EUV light beam is incident) of the mask. A variable blade has an arcshaped slit as disclosed in Japanese Patent Laid Open Application No. 2003045784. The width of the arcshaped slit needs to be partly variable.
Japanese Patent Laid Open Application No. 04196513 discloses a variable blade that operates in accordance with the transfer region of a mask. Such a variable blade operates in a synchronized manner with the velocity of a mask stage so as to obstruct light in the nontransfer region.
Particularly in the case of an EUV light source, a variable blade has an arcshaped slit. As shown in FIG. 10, an arcshaped illuminated region 105 is formed on a mask 101 by a variable blade having an arcshaped opening. A part 106 of an element pattern region 103 of the mask 101 has already been exposed. However, a test pattern region 104 has also been exposed. Whether the mask 101 has a test pattern or not, a shade region 102 is always exposed. Therefore, due to a defect in shading of the mask 101, a small amount of light is projected on the wafer. Since the element is rectangular and the light to be projected is arcshaped, however the blade is moved, this problem cannot be solved.
As shown in FIG. 11, masking blades 115 and 116 are disposed in a recess of a base 114 of a mask stage 112. This deteriorates the rigidity and accuracy of the mask stage 112. In addition, since the masking blades 115 and 116 are separated from a mask 111 by the thickness of the base 114, blur occurs. Therefore, when the center 113 of the light beam is in the position shown in FIG. 11, optically sufficient shading cannot be performed.
In order to increase productivity, the mask stage 112 moves at a high speed. Since the masking blades 115 and 116 are synchronized with the mask stage 112, they need to move at a high speed. Therefore, a linear motor is used as an actuator for them. Since the actuator is disposed in the recess of the base 114, the design is difficult. This deteriorates the reliability of the mask stage 112. In the case where the width of the slit is adjusted in accordance with the image height, more actuators are needed. This makes the design more difficult and further deteriorates the reliability.